In addition to changing the trigger that updates
zephyr_message.search_tsvector to use our new text search
configuration, it also now builds the tsvector on rendered_content
instead of content and fires on update of only the subject or
rendered_content columns.
This migration is expected to take a long time. The
checkpoint_segments parameter in postgresql.conf should be
temporarily raised (probably to 32) while it is running.
(imported from commit 4535438bb33ce1db2a74ecbe91efc52afdb568f1)
Zev Benjamin